Analyses using SPSS version 19 Chiara Haller, Harvard University

Analyses using SPSS version 19

Chiara Haller, Harvard University

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Objectives

Knowledge:

– How to use statistical analyses logically

– How to create/structure a dataset

– How to clean up the dataset

– How to create frequency tables

– Descriptive statistics:

– Graphs (box-plot, dispersion diagrams)

– Stratify the analysis

Literature: Introduction to SPSS (Andy Field)

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Data acquisition

Name Date of Birth Weight/height Sex

Type it directly into SPSS? Into Excel and - Import the data

- Copy the data into SPSS

Whatever you decide, keep a back up of your original dataset!!

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Missing data

Input a value which must not be confused with any other value.

For example giving it a coding which does not exist in the rest of

the data (i.e., -99).

Attention: Don’t forget to tell SPSS that these are missings!

means without correct coding

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The Computefunction

Calculate scores on

behalf of existing

variables

Example: Calculate

BMI on behalf of the

variables weight and

height

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Commande RECODE

Recode Variables

Example: Recode

height into 3

categories

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The syntax

It’s possible to keep all the analyses in a file Instead of OK, press PASTE, and your commands are being

opened as syntax, which can now be saved.

There are 3 windows you work with on SPSS:– Dataset: Variable view, data view– Output– Syntax

Each of these windows can be saved.

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Descriptive statistics

Mean

Variance / standard deviation

Minimum / Maximum

… (click options for more)

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Box-plot

Minimal Value

Mediane

Lower quartile (1st quartile

Upper quartile (3rd quartile)

Extreme Values

¼ (top 25%)

¼

¼«interquartile range»

¼ (bottom 25%)

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Scatter Plot

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Stratify the analysis

It is often useful to split a sample in several sub-samples

Three possibilities:– Split the file– Select the preferred observations– Perform the analysis by stratifying the variable

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Split files

Exercise:

Re-analyze the descriptive statistics

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Select the preferred observations

Exercise:

Re-analyze the descriptive statistics

THE END

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